1. Field of the Invention
The present invention relates to a Broadband Wireless Access (BWA) communication system using a multi-hop relay scheme. More particularly, the present invention relates to an apparatus and method for a signaling process of a Relay Station (RS) and a Base Station (BS) to perform an admission control for a service flow.
2. Description of the Related Art
Extensive research is being conducted to provide various Quality of Service (QoS) features with a data rate of about 100 Mbps in the fourth-generation (4G) communication system. The 4G communication system is evolving to provide mobility, high data rate transmission, and high QoS in a Broadband Wireless Access (BWA) communication system such as a Local Area Network (LAN) system and a Metropolitan Area Network (MAN) system. Example of the BWA system include systems based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16d and IEEE 802.16e standards, which are hereafter referred to as the IEEE 802.16d and IEEE 802.16e systems.
The IEEE 802.16d system and the IEEE 802.16e system use an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme.
FIG. 1 is a block diagram of a conventional IEEE 802.16e system.
Referring to FIG. 1, the IEEE 802.16e system has a multi-cell structure. The IEEE 802.16e system includes a cell 100, a cell 150, a BS 110 managing the cell 100, a BS 140 managing the cell 150, and a plurality of Mobile Stations (MSs) 111, 113, 130, 151 and 153. The signal exchange between the BSs 110 and 140 and the MSs 111, 113, 130, 151 and 153 is performed using an OFDM/OFDMA scheme. The MS 130 is located in a boundary region (i.e., a handover region) between the cells 100 and 150. When the MS 130 moves from the cell 100 of the BS 110 into the cell 150 of the BS 140 while communicating with the BS 110, the serving BS of the MS 130 is changed from the BS 110 to the BS 140.
Because a signaling communication between a stationary BS and an MS is performed through a direct link as illustrated in FIG. 1, the IEEE 802.16e system can provide a reliable wireless link between the BS and the MS. However, because the BS is stationary, the IEEE 802.16e system has low flexibility in constructing a wireless network. Accordingly, in the IEEE 802.16e system, it is difficult to provide an efficient communication service in a radio environment where traffic distribution or call requirements change frequently.
In order to address this problem, a stationary RS, a mobile RS or general MSs can be used to apply a multi-hop relay data transmission scheme to a cellular communication system such as the IEEE 802.16e system. The use of the multi-hop relay wireless communication system makes it possible to rapidly reconfigure a network in response to a change in the communication environment and to operate the entire wireless network more efficiently. For example, the multi-hop relay wireless communication system can expand a cell coverage area and increase a system capacity. When channel conditions between a BS and an MS are poor, an RS may be installed between the BS and the MS to establish a multi-hop relay link therebetween, thereby making it possible to provide the MS with a radio channel having better channel conditions. In addition, the multi-hop relay scheme is used in a cell boundary region with poor channel conditions, thereby making it possible to provide a high-rate data channel and to expand the cell coverage area.
FIG. 2 is a block diagram of a conventional BWA communication system that uses a multi-hop relay scheme to expand a BS coverage area.
Referring to FIG. 2, the multi-hop relay BWA communication system has a multi-cell structure. The multi-hop relay BWA communication system includes a cell 200, a cell 240, a BS 210 managing the cell 200, a BS 250 managing the cell 240, a plurality of MSs 211 and 213 located within the cell 200, a plurality of MSs 221 and 223 located in a region 230 outside the cell 200 of the BS 210 and communicating with the BS 210, an RS 220 providing a multi-hop relay path between the BS 210 and the MSs 221 and 223 located in the region 230, a plurality of MSs 251, 253 and 255 located in the cell 240, a plurality of MSs 261 and 263 located in a region 270 outside the cell 240 of the BS 250 and communicating with the BS 250, and an RS 260 providing a multi-hop relay path between the BS 250 and the MSs 261 and 263 located in the region 270. An OFDM/OFDMA scheme is used for communication among the BS 210 and 250, the RS 220 and 260, and the MSs 211, 213, 221, 223, 251, 253, 255, 261, and 263.
Although the MSs 211 and 213 located in the cell 200 and the RS 220 can directly communicate with the BS 210, the MSs 221 and 223 located in the region 230 cannot directly communicate with the BS 210. Therefore, the RS 220 serves the region 230 to relay signals between the BS 210 and the MSs 221 and 223. That is, the MSs 221 and 223 can communicate with the BS 210 through the RS 220. Further, the RS 260 and the MSs 251, 253, and 255 located in the cell 240 can directly communicate with the BS 250, the MSs 261 and 263 located in the region 270 cannot directly communicate with the BS 250. Therefore, the RS 260 serves the region 270 to relay signals between the BS 250 and the MSs 261 and 263. That is, the MSs 261 and 263 can communicate with the BS 250 through the RS 260.
FIG. 3 is a block diagram of a conventional BWA communication system that uses a multi-hop relay scheme to increase a system capacity.
Referring to FIG. 3, the multi-hop relay BWA communication system includes a BS 310, a plurality of MSs 311, 313, 321, 323, 331, and 333, and RSs 320 and 330 providing multi-hop paths between the BS 310 and the MSs 311, 313, 321, 323, 331, and 333. The BS 310, the MSs 311, 313, 321, 323, 331, and 333, and the RSs 320 and 330 communicate with one another using an OFDM/OFDMA scheme. The BS 310 manages a cell 300. The RSs 320 and 330 and the MSs 311, 313, 321, 323, 331, and 333 that are in the cell 300 directly communicate with the BS 310.
When some MSs 321, 323, 331, and 333 are in a boundary region of the cell 300, Signal-to-Noise Ratios (SNRs) of direct links between the BS 310 and the MSs 321, 323, 331, and 333 may be low. In this case, the RS 320 relays traffic between the BS 310 and the MSs 321 and 323. The MSs 321 and 323 communicate traffic with the BS via the RS 320. Further, the RS 330 relays traffic between the BS 310 and the MSs 331 and 333. The MSs 331 and 333 communicate traffic with the BS via the RS 330. The RSs 320 and 330 provide high-rate data paths to the MSs 321, 323, 331, and 333, thereby increasing the effective transfer rates of the MSs 321, 323, 331, and 333 and the capacity of the multi-hop relay BWA communication system.
In the multi-hop relay BWA communication systems of FIGS. 2 and 3, one or more of the RSs 220, 260, 320, and 330 may be infrastructure RSs that are installed by a service provider and managed by the BSs 210, 250, and 310, or may be client RSs that operate as Subscriber Stations (SSs), MSs, or RSs. In addition, one or more of the RSs 220, 260, 320, and 330 may be stationary RSs, nomadic RSs (e.g., notebooks), or mobile RSs having mobility similar to an MS.
In the multi-hop relay BWA communication system, if a new service flow for an MS is created or the QoS parameter of the current service flow for the MS is changed while the MS is communicating with a BS directly or through an RS, the BS and the RS must be able to support the parameter of the new service flow or the new QoS parameter of the current service flow.
The service flow parameter of the MS may be determined by a QoS policy server in the network. In order to determine the service flow parameter, the QoS policy server obtains supportable parameter information from the BS and the RS. Herein, the supportable parameter information is obtained through the admission control of the corresponding nodes (i.e., the BS and the RS).
What is therefore required is a signaling process by which the corresponding nodes in the data transmission path of the MS can perform the admission control when a new service flow for the MS is created or the parameter of the current service flow for the MS is changed in the multi-hop relay system BWA communication system.